The constant development of optical fiber technology has given rise to an increasing demand for germanium and also of arsenic.
As high-germanium raw materials are available only in restricted quantities it is necessary to process raw materials which are low in germanium. The solutions resulting from the leaching of these raw materials contain small amounts of germanium and considerable quantities of other materials.
Different processes have been used thus far for separating and enriching germanium; these processes include precipitation with tannin and subsequent separation., extraction/re-extraction and ion exchange processes. The precipitation is very expensive and depends highly on the tannin which, as a natural product, varies in quality. In the extraction/re-extraction processes the organic phase must be retreated before it is reused. In ion exchange processes in columns, the ion exchange resin columns must be regenerated.
From the U.S. Pat. No. 3,779,907 it is known that solutes in aqueous systems can be extracted and can be processed for a recovery of the valuable substance. In the above-mentioned process a solute in an aqueous medium is removed by contacting the solution with a water-in-oil emulsion which consists of an aqueous inner phase which renders the solute unable to leave and a surrounding organic hydrophobic outer phase, which contains a surfactant.
That treatment results in a concentration gradient and causes the solute to penetrate the outer phase and to be transformed in the inner phase to a substance which is unable to penetrate the outer phase. After that contact, the emulsion is separated from the aqueous solution which has been depleted of the solute, and the emulsion can then be regenerated. The process of regenerating the emulsion comprises breaking the emulsion.
Certain reagents can be added to the solvent to render the organic phase permeable for substrates. The permeability may be selectively adjusted by the selection of the reagents and of the solvents.
Published German Application No. 28 29 163 discloses a process of recovering solutes from an aqueous solution by liquid membrane technology. In that process the emulsion which has been separated is exposed to an electrostatic field in order to coalesce (break) the droplets of the aqueous inner phase. The voltage gradient in the electrostatic coalescing zone exceeds about 1 kV/cm.
Numerous water-immiscible solvents have been proposed for the organic phase of the liquid membrane emulsion, which contain also a surfactant, such as sorbitemonolauric ester. The known process can be used to extract anionic and cationic substances but neither germanium nor arsenic has been disclosed or taken into account.
Published German Application No. 33 18 109 discloses a process of recovering zinc from heterogeneous sewage compositions. That process also comprises an extraction by means of a liquid membrane emulsion. The aqueous inner phase of the liquid membrane emulsion consists of an aqueous 1N to 6N mineral acid, preferably sulfuric acid, and the substances added to the membrane-forming phase include a surfactant consisting of sorbitmonolauric ester and a transfer agent consisting, e.g., of an organic phosphorous compound, such as bis-(2-ethylhexyl) phosphoric ester.